The present invention relates to a method of producing a ceramic veneer that is coilable in unfired condition and thereby may be decorated and fired as an endless strip. The ceramic veneer is formed of a laminar base material consisting of inorganic fibers, preferably a glass-fiber mat or fleece that is coated on both sides with ceramic material, preferably on one side with a paste layer and on the other side with a glaze layer. For the production of the veneer, organic ceramic slips containing organic binders are applied on the base material and dried while in free suspension.
In order to provide large-surface construction units with ceramic coatings, there is an increased need for ceramic veneering. Although different approaches for producing such veneers have been selected, they remain unsatisfactory in some areas in terms of application characteristics and/or the economy of production processes.
In U.S. Pat. No. 2,307,332, the production of ceramic veneers is described, where a fine-particle ceramic paste containing a fusible binder is inserted into a furnace on a combustible support. During firing, only the binder melts thereby binding the ceramic particles together. It was actually also suggested to imbed a reinforcement layer, e.g., a metal screen or mineral wool in the paste. However, it was not possible to thus increase the strength of the veneers. In unfired condition, such veneers cannot be coiled or rolled up without damage and in this form subjected to further refinement steps.
According to German Patent 20 61 105, ceramic veneers are produced by applying a thinly fluid ceramic slip on a water-permeable or absorbent combustible support medium and subsequent combined firing, whereby the support burns up. In order to avoid crack formations during predrying of the slip layer, a layer of glass or mineral fibers was placed in the slip layer applied on the combustible support according to German Patent 22 01 435; a patent of addition to DE 20 61 105. It was possible to apply a second slip layer on the fiber layer; in addition, a glaze-producing paste could be applied to the layer that would be on top.
The use of the combustible support is also considered a requirement for systems containing a fiber layer, in order to make coating and drying possible. However, it appeared that the combustion of the support during firing was not without problems. The ceramic veneers of the type described above are also not coilable in unfired condition, since the lack of binders with an elastifying effect necessarily results in cracking during coiling and uncoiling.
Ceramic plates or tiles consisting of a ceramic paste layer, a fleece (non-woven fabric) or a cloth, e.g., of glass fibers, rolled on the moist paste string, optionally decorated, and with a glaze placed on top, are known from German Published Patent Application DE-OS 32 46 270. However, this document does not suggest how such systems in the form of veneers can be fabricated. A veneer consisting of at least two slip layers of different composition and a glass fleece arranged on the upper slip layer and/or between two slip layers is the object of German Patent DE-PS 26 39 522. For the production of such a veneer, the slips are applied on an endless rotating strip, the glass fleece is then added, and the composite is subsequently fired in the furnace. The unfired article is unsuitable for coiling and instead should be fired directly in connection with drying.
An unfired glaze in the form of a film where the starting materials for the glaze to a large extent, preferably predominantly, and optimally completely, are in fiber form is known from German Patent 19 36 888. In so far as particle-shaped starting materials for the glaze are also used, they are applied in the form of a suspension containing 0.1 to 2 percent by weight based on the dispersed fatty substances on a fleece, a tissue or texture, e.g., by soaking these in the suspension. In this document, reference is made to the fact that a higher concentration of binders is unfavorable, since they decompose during firing and cause blisters to form in the glaze. The object of DE-PS 19 36 888 thus solely focuses on an unfired glaze film and not on a ceramic veneer predominantly composed of particle-shaped ceramic materials. To the extent that the unfired glaze film in DE-PS 19 36 888, in addition to the fiber ingredients, also contains particle-shaped glaze ingredients, these must be very similar in composition to those of the fiber material. Thus, the selection possibilities of glaze ingredients and their composition are very restricted.
In EP-B 159,514, a coating-layer material on fleece or woven fabric is disclosed, displaying a coating of powdery inorganic material only on one side. The coating contains at least 6 percent by weight of completely dry organic binders. The coating-layer material, however, is not subjected to any ceramic baking. As a result, problems in connection with blister formation through decomposition of the polymer and/or an unsatisfactory compound of fibrous materials and particles do not occur. For the production of the coating-layer material, a glass-fiber fleece is, for example, coated on a doctor knife apparatus with a paste consisting of the inorganic powder, a plastic dispersion, and usual additives, and dried. Applicable are fleeces with a weight per unit area ranging between 35 and 350 g/m.sup.2. The coating weights range between 150 to 450 g/m.sup.2.